This invention relates to optical disks such, for example, as a CD, a CD-ROM, a CD-R, a CD-RW, a CD-I, a MD and a DVD and, more particularly, to optical disks having two areas of different recording densities. This invention relates also to optical disks having areas of different functions and to a method of manufacturing such optical disks and also to a method of recording information on such optical disks.
Optical disks such as a CD, a CD-ROM and a CD-R having a standard recording density have a track pitch of 1.6 xcexcm and a linear velocity of 1.2 m/s to 1.4 m/s. With the recent tendency to using a laser beam spot of a smaller diameter, optical disks having a higher recording density have been developed. For example, a DVD-ROM has a track pitch of 0.74 xcexcm and linear velocity of 3.94 m/s and has a recording capacity which is seven times as large as a CD.
In case a large amount of data such as a moving picture data is to be recorded in coping with the tendency to increasing the recording capacity of an optical disk, an optical disk having a high recording density may be used.
An optical disk drive device which can cope with media having a high recording density can drive also an optical disk having a lower recording density whereas an optical disk drive device which can reproduce only a CD having a standard recording density cannot drive an optical disk having a high recording density. For this reason, when an optical disk having a high recording density is used, conventional CD drive devices cannot reproduce such optical disk so that drive devices which can reproduce it are limited.
It is, therefore, a first object of the present invention to provide an optical disk which has a much larger recording capacity than a conventional optical disk of a standard recording density and yet is applicable also to a drive device which can reproduce only the conventional optical disk of the standard recording density.
Known also in the art of optical disks is one having areas of different functions. For example, Japanese Patent Application Laid-open 9-7223 discloses an optical disk having a ROM area used for read-only purpose and a RAM area which can be rewritten. This optical disk has advantages of both a read-only disk and a rewritable disk in that a large amount of copies can be produced from a software by using the ROM area while data can be written in the RAM area.
In this type of optical disk, information recorded in the ROM area cannot be erroneously overwritten but information recorded in the RAM area can be erroneously overwritten. In a floppy disk, overwriting can be inhibited but this can be made only for the entire disk and not for only a part of data which is important.
It is, therefore, a second object of the invention to provide an optical disk in which a recording mode can be selected depending upon the degree of importance of information.
It is a third object of the invention to provide a method for recording information on this optical disk.
It is a fourth object of the invention to provide a method for manufacturing this optical disk.
For achieving the first object of the invention, there is provided an optical disk comprising a first area of a standard recording density formed on an inner peripheral side of the optical disk, a second area of a higher recording density than the first area formed on an outer peripheral side of the optical disk, and a program recording area provided in each of the first and second areas, said program recording area being capable of recording a program independently of each other program recording area.
According to the invention, by using a different mode of recording for each of the first and second areas such as recording a standard program in the first area and a higher degree of program in the second area, a substantial degree of program can be reproduced with a conventional standard optical disk drive so that the optical disk according to the invention can provide interchangeability between the conventional optical disk drive and an optical disk drive exclusively used for an optical disk of a high recording density. Moreover, by providing a high recording density area in the outer peripheral side of the optical disk, the recording capacity can be increased substantially as compared with the conventional CD and the data transfer rate can also be increased.
Either or both of the first and second areas may be constructed as a read-only area. Likewise, either or both of the first and second areas may be constructed as an area which is capable of both writing and reading.
In one aspect of the invention, depth from a surface on which laser beam is irradiated to a recording surface of the second area is smaller than depth from the surface on which laser beam is irradiated to a recording surface of the first area. By this arrangement, a layer of a high refractive index may be made thinner in the high recording density area than in the standard recording density area and, accordingly, the amount of deviation of a beam spot caused by deflection or inclination of an optical disk can be reduced.
In another aspect of the invention, a border area between the first area and the second area is formed as a mirror area where all laser beam is reflected. By this arrangement, the largest level of reflected beam can be obtained in this mirror area and, accordingly, this area can be distinguished from the other areas by a simple signal processing. This arrangement is particularly effective in the high speed search operation.
In another aspect of the invention, a border area between the first area and the second area is an area where recording density changes gradually from the standard recording density to the higher recording density. By this arrangement, a tracking control can be made by gradually changing a servo parameter from the first area to the second area.
In another aspect of the invention, the first and second areas have a lead-in area, a program area and a lead-out area and TOC information of the program area of each area is recorded in the lead-in area of each area. By this arrangement, each area can be controlled independently and a drive device which can reproduce only an optical disk of the standard recording density can be accessed as if the optical disk was one having the first area only.
In still another aspect of the invention, the first area has a lead-in area and a program area and the second area has a program area and a lead-out area, TOC information of the program area of the first and second areas being recorded in the lead-in area of the first area. By this arrangement, TOC information of all areas can be obtained by accessing the first lead-in area only so that initial time of the drive device can be saved.
For achieving the second object of the invention, there is provided an optical disk comprising a rewritable area (hereinafter refereed to as xe2x80x9cRAM areaxe2x80x9d in which recorded information can be rewritten and a write once area (hereinafter referred to as xe2x80x9cWO areaxe2x80x9d in which information can be recorded only once.
The optical disk may further comprise a read-only area (hereinafter refereed to as xe2x80x9cROM areaxe2x80x9d) capable of only reading recorded information.
According to this aspect of the invention, processing, addition and renewal of data can be made in the RAM area and important information for which processing has been completed and no more change needs to be made can be recorded in the WO area. Therefore, overwrite inhibit can be applied only to important data while freedom of rewriting is retained, so that the scope of information recording operation can be significantly broadened.
By further providing the ROM area, a further broadened scope of use can be ensured such that a predetermined program may be recorded in the ROM area and data input in accordance with this program may be processed in the RAM area and result of the processing may be recorded in the WO area.
For achieving the third object of the invention, there is provided a method for recording information in the optical disk as described above comprising a step of recording information which has been rewritten in the rewritable area in the write once area as overwrite inhibit information in accordance with a predetermined command.
For achieving the fourth object of the invention, there is provided a method for manufacturing the optical disk as described above comprising steps of a first masking step of covering a portion of an optical disk substrate other than a firs t area with a masking material, a step of forming an alloy layer consisting of an optomagnetic material or a phase changing material on the substrate masked by the first masking step, a first masking removing step of removing the masking material from the substrate formed with the alloy layer, a second masking step of covering a portion of the substrate other than a second area which is different from the first area with a masking material, a step of forming a dyestuff layer which changes with heat on the substrate masked by the second masking step, a second masking removing step of removing the masking material from the substrate formed with the dyestuff layer, and a step of forming a reflecting layer on the substrate formed with the alloy layer in the first area and the dyestuff layer in the second area.
According to this aspect of the invention, the RAM area can be formed by providing an alloy layer consisting of an optomagnetic material or a phase changing material and the WO area can be formed by providing a dyestuff layer which changes with heat. Accordingly, by performing masking in accordance with these areas to selectively form the alloy layer and the dyestuff layer, the optical disk of this aspect of the invention can be produced.
These and other objects and features of the invention will become apparent from the description made below with reference to the accompanying drawings.